I used this tutorial to make an RFID blocking wallet for my credit cards today. Instead of using heavy duty aluminum foil I used Mylar. I didn't have any pretty duct tape so my wallet is zebra striped.
As soon as I find some pretty duct tape I can make another one now that I know how to do it. I used to carry my credit cards in an ugly mylar pouch in my billfold so this at least is an improvement.